/* 
 * This file is part of the Echo File Transfer Library (hereinafter "EFTL").
 * Copyright (C) 2002-2005 NextApp, Inc.
 *
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 */

package org.openinsula.arena.echo2.component.provider.ui;

/**
 * Factory for MultipartUploadSPI implementations. This class is responsible for
 * discovery of MultipartUploadSPI implementations and creation of new instances
 * on demand.
 * 
 * Custom MultipartUploadSPI implementations may be configured by calling
 * <code>System.setProperty(MultipartUploadSPI.SYSTEM_PROPERTY_NAME, "com.example.CustomMultipartUploadSPI")</code>
 * from within an application entry point. The given fully qualified
 * implementation class <strong>must</strong> implement a public default (no
 * argument) constructor.
 * 
 */
public class MultipartUploadFactory {

	protected static final Class DEFAULT_MULTIPART_UPLOAD_SPI = JakartaCommonsFileUploadProvider.class;

	private static MultipartUploadSPI INSTANCE = null;

	/**
	 * Attempts to find the configured MultipartUploadSPI implementation class
	 * by checking for the System property setting
	 * <code>MultipartUploadSPI.SYSTEM_PROPERTY_NAME</code>. If the property
	 * is null, a default implementation is created and returned.
	 * 
	 * @return the implementation
	 */
	public static MultipartUploadSPI getMultipartUploadSPI() {
		if (INSTANCE == null) {
			INSTANCE = newInstance(getImplementationClass());
		}
		return INSTANCE;
	}

	/**
	 * Attempts to locate the class defined by the System property
	 * nextapp.echo2.webcontainer.filetransfer.MultipartUploadSPI
	 * 
	 * @return the <code>MultipartUploadSPI</code> class if found, otherwise
	 * the default implementation.
	 */
	private static Class getImplementationClass() {
		String implementationClassName = System.getProperty(MultipartUploadSPI.SYSTEM_PROPERTY_NAME);

		if (implementationClassName != null) {
			try {
				return Class.forName(implementationClassName);
			}
			catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
		else {
			return DEFAULT_MULTIPART_UPLOAD_SPI;
		}

	}

	private static MultipartUploadSPI newInstance(Class clss) {
		try {
			return (MultipartUploadSPI) clss.newInstance();
		}
		catch (Exception e) {
			throw new RuntimeException(e);
		}
	}
}
